Triglyceride Paradox Is Related to Lipoprotein Size, Visceral Adiposity and Stearoyl-CoA Desaturase Activity in Black Versus White Women

Abstract

Rationale: In black women, triglycerides are paradoxically normal in the presence of insulin resistance. This relationship may be explained by race-related differences in central adiposity and SCD (stearoyl-CoA desaturase)-1 enzyme activity index.

Objective: In a cross-sectional study, to compare fasting and postprandial triglyceride-rich lipoprotein particle (TRLP) concentrations and size in black compared with white pre- and postmenopausal women and determine the relationship between TRLP subfractions and whole-body insulin sensitivity, hepatic and visceral fat, and SCD-1 levels.

Methods and results: In 122 federally employed women without diabetes mellitus, 73 black (58 African American and 15 African immigrant) and 49 white; age, 44±10 (mean±SD) years; body mass index, 30.0±5.6 kg/m2, we measured lipoprotein subfractions using nuclear magnetic resonance. Hepatic fat was measured by proton magnetic resonance spectroscopy, insulin sensitivity index calculated by minimal modeling from a frequently sampled intravenous glucose test, and red blood cell fatty acid profiles were measured by gas chromatography and were used to estimate SCD-1 indices. Hepatic fat, insulin sensitivity index, and SCD-1 were similar in black women and lower than in whites, regardless of menopausal status. Fasting and postprandial large, medium, and small TRLPs, but not very small TRLPs, were lower in black women. Fasting large, medium, and very small TRLPs negatively correlated with insulin sensitivity index and positively correlated with visceral and hepatic fat and SCD-1 activity in both groups. In multivariate models, visceral fat and SCD-1 were associated with total fasting TRLP concentrations (adjR2, 0.39; P=0.001). Black women had smaller postprandial changes in large (P=0.005) and medium TRLPs (P=0.007).

Conclusions: Lower visceral fat and SCD-1 activity may contribute to the paradoxical association of lower fasting and postprandial TRLP subfractions despite insulin resistance in black compared with white pre- and postmenopausal women. Similar concentrations of very small TRLPs are related to insulin resistance and could be important mediators of cardiometabolic disease risk in women.

Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01809288.

Keywords: continental population groups; humans; insulin resistance; liver; obesity.

Conflict of interest statement

DISCLOSURES

I STC certify that neither I nor my co-authors have any conflicts of interest.

Figures

Figure 1.. Fasting triglyceride-rich lipoprotein particle (TRLP) concentrations

(A) Bar graph of TRLP concentrations after a 10-12 hour overnight fast; very small (black bar), small (grey bar with black dots), medium (light gray), large (white); Violin plots of large (B), medium (C), small (D), and very small (E) TRLP concentrations in black (dark gray, n=73) and white (white, n=49) pre- and post-menopausal women. The shape of the violin is the frequency distribution of the data, the solid black line represents the median and the dotted black line represents the interquartile range. Mann-Whitney tests were used to compare variables by race.

Figure 2.. Postprandial triglyceride-rich lipoprotein particle (TRLP) concentrations.

Concentrations of large (A-B), medium (C-D), small (E-F), and very small (G-H) TRLPs during the 5-hour mixed meal test in black (solid squares and lines, n=68) and white (white circles and lines, n=42) pre- and post-menopausal women. Data presented mean±SEM. Mixed effects models were used to analyze TRLP over time (within-subject factor of time; between-subject factor of race; time x race interaction).

Figure 3.. The change in postprandial triglyceride-rich lipoprotein particle (TRLP) concentrations.

The change in large (A-B), medium (C-D), small (E-F), and very small (G-H) TRLP concentrations during the 5-hour mixed meal test in black (solid squares and lines, n=68) and white (white circles and lines, n=42) pre- and post-menopausal women. Data presented mean±SEM. Mixed effects models were used to analyze the change in TRLP over time (within-subject factor of time; between-subject factor of race; time x race interaction).

Figure 4.. The relationship of fasting total triglyceride-rich lipoprotein particle (TRLP) concentrations with markers of insulin resistance and de novo lipogenesis.

Scatterplot of natural log (ln) of total TRLP and ln visceral fat (A-B), ln hepatic fat (C-D), and ln stearoyl-CoA desaturase activity (SCD-116) black (black squares) and white (white circles) women. Data presented as individual data points with corresponding regression line and 95% confidence interval in dotted line. Spearman correlations with Bonferroni corrections were used to determine correlation coefficients (r).